arXiv subjects

G. Schwiete

Publications and source records attributed to G. Schwiete.

23 records · Page 2Linked to original sources

arXiv2005

Supersymmetry for disordered systems with interaction

Considering disordered electron systems we suggest a scheme that allows us to include an electron-electron interaction into a supermatrix sigma-model. The method is based on replacing the initial model of interacting electons by a fully supersymmetric model. Although this replacement is not exact, it is a good approximation for a weak short range interaction and arbitrary disorder. The replacement makes the averaging over disorder and further manipulations straightforward and we come to a supermatrix sigma-model containing an interaction term. The structure of the model is rather similar to the replica one, although the interaction term has a different form. We study the model making perturbation theory and renormalization group calculations. We check the renormalizability of the model in the first loop approximation and in the first order in the interaction. In this limit we reproduce the renormalization group equations known from earlier works. We hope that the new supermatrix sigma-model may become a new tool for non-perturbative calculations for disordered systems with interaction.

cond-mat.mes-hall↗

arXiv2004

Bosonization for disordered and chaotic systems

Using a supersymmetry formalism, we reduce exactly the problem of electron motion in an external potential to a new supermatrix model valid at all distances. All approximate nonlinear sigma models obtained previously for disordered systems can be derived from our exact model using a coarse-graining procedure. As an example, we consider a model for a smooth disorder and demonstrate that using our approach does not lead to a 'mode-locking' problem. As a new application, we consider scattering on strong impurities for which the Born approximation cannot be used. Our method provides a new calculational scheme for disordered and chaotic systems.

cond-mat.mes-hall↗

arXiv2003

Tunneling density of states of granular metals

We investigate the effect of Coulomb interactions on the tunneling density of states (DOS) of granular metallic systems at the onset of Coulomb blockade regime in two and three dimensions. Using the renormalization group technique we derive the analytical expressions for the DOS as a function of temperature $T$ and energy $ε$. We show that samples with the bare intergranular tunneling conductance $g^0_{\scriptscriptstyle T}$ less than the critical value $g_{\scriptscriptstyle T}^{\scriptscriptstyle C}=(1/2πd) \ln(E_{\scriptscriptstyle C}/δ)$, where $E_{\scriptscriptstyle C}$ and $δ$ are the charging energy and the mean energy level spacing in a single grain respectively, are insulators with a {\it hard gap} in the DOS at temperatures $T\to 0$. In 3d systems the critical conductance $g_{\scriptscriptstyle T}^{\scriptscriptstyle C}$ separates insulating and metallic phases at zero temperature, whereas in the granular films $g_{\scriptscriptstyle T}^{\scriptscriptstyle C}$ separates insulating states with the hard (at $g^0_{\scriptscriptstyle T} g_{\scriptscriptstyle T}^{\scriptscriptstyle C}$) gaps. The gap in the DOS begins to develop at temperatures $ T^* \sim E_{\scriptscriptstyle C} g_{\scriptscriptstyle T}^{\scriptscriptstyle 0} \exp (-2πd g_{\scriptscriptstyle T}^{\scriptscriptstyle 0})$ and reaches the value $Δ\sim T^*$ at $T\to 0$.

cond-mat.mes-hall↗

arXiv2003

Weak Localization and Integer Quantum Hall Effect in a Periodic Potential

We consider magnetotransport in a disordered two-dimensional electron gas in the presence of a periodic modulation in one direction. Existing quasiclassical and quantum approaches to this problem account for Weiss oscillations in the resistivity tensor at moderate magnetic fields, as well as a strong modulation-induced modification of the Shubnikov-de Haas oscillations at higher magnetic fields. They do not account, however, for the operation at even higher magnetic fields of the integer quantum Hall effect, for which quantum interference processes are responsible. We then introduce a field-theory approach, based on a nonlinear sigma model, which encompasses naturally both the quasiclassical and quantum-mechanical approaches, as well as providing a consistent means of extending them to include quantum interference corrections. A perturbative renormalization-group analysis of the field theory shows how weak localization corrections to the conductivity tensor may be described by a modification of the usual one-parameter scaling, such as to accommodate the anisotropy of the bare conductivity tensor. We also show how the two-parameter scaling, conjectured as a model for the quantum Hall effect in unmodulated systems, may be generalized similarly for the modulated system. Within this model we illustrate the operation of the quantum Hall effect in modulated systems for parameters that are realistic for current experiments.

cond-mat.mes-hall↗

arXiv2000

Coherent production of hard dijets on nuclei in QCD

We formulate the perturbative QCD approach to coherent diffractive dijet production in pion-nucleon and pion-nucleus collisions at high energy. For hard dijets the Pomeron splitting mechanism in which both helicity amplitudes are proportional to the unintegrated gluon structure function of the proton and the pion distribution amplitude is shown to dominate. In nuclear diffraction multiple Pomeron splitting components are found to give antishadowing contributions at large jet momentum. To leading twist there is an exact cancelation of effects of nuclear attenuation and antishadowing/broadening of multiple Pomeron splitting contributions. The next-to-leading higher twist correction driven by nuclear rescatterings is calculable in hard QCD and proves to be numerically very large. We argue that large higher twist effects do not preclude the determination of gross features of the pion distribution amplitude. Our results on the atomic mass number and momentum dependence of dijet cross sections agree well with the preliminary findings from the E791 experiment.

hep-ph↗